Gas delivery manifold and processed material discharge assembly for rotary kiln

ABSTRACT

A rotary kiln is disclosed with a rotary firing hood mounted concentrically over the material discharge end of the kiln to rotate with the kiln. A main burner assembly projects axially through a neck formed by a rear wall of the hood and a plurality of burners project radially through the kiln shell. Fuel gas conducting tubes for supplying the kiln shell burners, are mounted on the outer periphery of the kiln shell and extend axially through the hood and rear wall thereof. The fuel tubes each have portions that project radially inward along an outer surface of the hood rear wall and axially away from the rear wall to an annular fuel gas manifold box mounted close around the hood rear wall neck. The annular manifold box has a pair of axially spaced radial walls connected to rotate with the rotary hood and a nonrotating outer sleeve connected to a stationary fuel gas delivery conduit. An annular air manifold box, similar in construction to the fuel gas manifold box, is mounted close around the axially extending portions of the fuel tubes and between the fuel gas manifold box and the rear wall of the firing hood. Air conducting tubes mounted on the kiln shell also extend axially through the rotary hood and rear wall thereof and have portions which project radially inward and axially away from the rear wall to the annular air manifold box. The kiln is provided with a pair of radial discharge ports, circumferentially spaced 180* apart, for discharging processed material twice each revolution of the kiln. The air and fuel gas tubes are arranged along the kiln shell in two groups, with each group of tubes being on one side of the kiln and between the pair of kiln discharge ports to be spaced away from hot processed material discharged through the ports.

United States Patent Rossi [451 May 9, 1972 [54] GAS DELIVERY MANIFOLDAND PROCESSED MATERIAL DISCHARGE ASSEMBLY FOR ROTARY KILN PrimaryE.\-aminerJohn .l. Camby A!1orne \-Arth ur M. Streich, Robert B. Bensonand John P. Hines [5 7] ABSTRACT A rotary kiln is disclosed with arotary firing hood mounted F m l concentrically over the materialdischarge end of the kiln to rotate with the kiln. A main burnerassembly projects axially through a neck formed by a rear wall of thehood and a plurality of burners project radially through the kiln shell.Fuel gas conducting tubes for supplying the kiln shell burners. aremounted on the outer periphery of the kiln shell and extend axiallythrough the hood and rear wall thereof. The fuel tubes each haveportions that project radially inward along an outer surface of the hoodrear wall and axially away from the rear wall to an annular fuel gasmanifold box mounted close around the hood rear wall neck. The annularmanifold box has a pair of axially spaced radial walls connected torotate with the rotary hood and a nonrotating outer sleeve connected toa stationary fuel gas delivery conduit. An annular air manifold box,similar in construction to the fuel gas manifold box, is mounted closearound the axially extending portions of the fuel tubes and between thefuel gas manifold box and the rear wall of the firing hood. Airconducting tubes mounted on the kiln shell also extend axially throughthe rotary hood and rear wall thereof and have portions which projectradially inward and axially away from the rear wall to the annular airmanifold box. The kiln is provided with a pair of radial dischargeports, circumferentially spaced 180 apart, for discharging processedmaterial twice each revolution of the kiln. The air and fuel gas tubesare arranged along the kiln shell in two groups, with each group oftubes being on one side of the kiln and between the pair of kilndischarge ports to be spaced away from hot processed material dischargedthrough the ports.

8 Claims, 3 Drawing Figures PATENTEDMAY 9 I972 SHEET 1 BF 3 BACKGROUNDOF THE INVENTION 1. Field of the Invention This invention relates torotary kilns, used for such purposes as'reducing iron ore to a lowerstate of oxidation, and having nozzles mounted on the outer surface ofthe kiln to project radially through the kiln shell and inject air andfuel into the kiln at axially spaced locations along the length of thekiln. In particular the present invention relates to an assembly fordelivering air and gaseous fuel from stationary conduits to conduitsmounted on the kiln shell to rotate therewith, and for dischargingprocessed material from the kiln.

2. Description of the Prior Art Rotary kilns for such as reducing ironore to a lower state of oxidation and having nozzles projecting througha kiln shell for injecting air into the kiln, are disclosed in priorpatents, for example U.S. Pat. No. 1,216,667 of 1917; U.S. Pat. No.1,760,078 of 1930; and U.S. Pat. No. 2,344,440 of 1944. Such kilnsdisclose seals between nonrotating conduit structures and rotatingconduit structures having a diameter larger than the diameter of thekiln. It has always been difficult to construct good seals of such largediameter because thermal expansion is proportionately greater for largersizes, and it is more difficult to provide the dimension tolerances andsurface finishes needed for effective seals. For conduits and nozzlesdelivering only air to the kiln, the problem was not serious as there isno danger involved if the seals leak air externally of the kiln and theeconomic loss from leaking air is not great.

Early examples of prior art patents disclose constructions which avoideddelivering gaseous fuel through such distribution systems for leaks ofcombustible gases could involve both danger and significant economicloss. 1

Early prior art patents disclose other ways for admitting fuel to thekiln. The three previously mentioned prior art patents introduced areducing atmosphere into the kiln by injecting fuel through the usualaxial burner projecting into the material discharge end of the furnace,and the first two of those references also disclose includingcombustible material with the charge material fed to the furnace.

Other ways have been disclosed by priorart to inject gaseousfuel intosuch a kiln without creating a need for such large diameter seals. U.S.Pat. No. 1,797,130 of 1931 accomplishes such fuel injection with asingle annular tube extending along the central axis of the kiln andhaving nozzles which project radially outward from the tube. U.S. Pat.Nos. 2,848,]98; 3,l82,980; and 3,196,938 provide several axiallyextending fuel conduits inside the kiln shell. U.S. Pat. No. 3,01 1,772discloses a double wall kiln with gaseous flue being delivered to thespace between the walls. The kiln constructions disclosed in this groupof patents all involve seals between stationary and rotating fueldelivery conduits having a diameter smaller than the outer diameter ofthe assembly but all these constructions have two disadvantages. Onedisadvantage is that-the gaseous fuel conduits are not kept cool byexposure to the atmosphere of surrounding air and a second disadvantageis that such conduits are hidden from view and cannot therefore beinspected. while the kiln is in operation.

U.S. Pat. Nos. 3,132,023 of 1964 and 3,235,375 do disclose constructionsin which both air and fuel conduits carried to rotate with the kiln areexternal to the kiln and a joint between the rotating and nonrotatingconduits does not require seals having a diameter larger than the kiln.The constructions disclosed in these two patents however (and U.S. Pat.Nos. 2,848,198; 3,196,938; and 3,0l 1,772 of the previous group)discharge processed material from the kiln through an opening central ofthe seal and therefore necessarily smaller than the diameter of thekiln. With such a construction the kiln must either contain a relativelylarge charge in order for material to flow over a dam formed by thedischarge header (as with.S. Pat. No. 3,235,375); or be provided withinternal lifters (as with U.S. Pat. Nos. 3,848,198; 3,011,772 and3,196,938); or a double shell kiln and lifters for moving processedmaterial back to the feed end of the kiln for discharge (as with U.S.Pat. No. 3, l 32,023).

SUMMARY OF THE INVENTION It is an object of the present invention toprovide a new and improved gas delivery manifold and processed materialdischarge assembly in which gases from stationary sources of supply aredelivered to tubesmounted on the outer periphery of a kiln to rotatewith kiln, through sealed annular manifolds of diameter smaller than thekiln and mounted in spaced axial alignment relative to the discharge endof the kiln, and having provision for discharging processed materialradially outward from the inner periphery of the kiln without directexposure of the tubes to the hot processed material discharging from thekiln.

According to a preferred embodiment of the present invention a rotarykiln is provided with a rotary firing hood mounted concentrically overthe material discharge end of the kiln to rotate with the kiln. A mainburner projects axially through a neck formed by a rear wall of the hoodand a plurality of burners project radially through the kiln shell. Fuelgas conducting tubes for supplying the burners projecting through thekiln shell, are mounted on the outer periphery of the kiln shell andextend axially through the rotary hood and rear wall thereof. The fueltubes each have portions that project radially inward along an outersurface of the hood rear wall and axially away from the rear wall inproximity to the burner assembly, to an annular fuel gas manifold boxmounted around the burner assembly. The annular manifold box has a pairof axially spaced radial walls attached to rotate with the burnerassembly and a nonrotating outer sleeve connected to a stationary fuelgas delivery conduit. An annular air manifold box, similar inconstruction to the fuel gas manifold box, is mounted around the axiallyextending portions of the fuel tubes and between the fuel gas manifoldbox and the rear wall of the firing hood. Air conducting tubes mountedon the kiln shell also extend axially through the hood and rear wallthereof. The air tubes have portions which project radially inward alongthe outer surface of the hood rear wall and axially away from the rearwall to the annular air manifold box. The kiln is provided with a pairof radial discharge ports, circumferentially spaced apart, fordischarging processed material twice each revolution of the kiln. Theair and fuel gas tubes are arranged along the kiln shell in two groups,with each group of tubes being on one side of the kiln and between thepair of discharge ports. A stationary hood defining a single downwarddischarge passage, encloses the outer periphery of the rotary firinghood. Processed material therefore discharges from the kiln radiallydownward between the groups of tubes and down through the singledischarge passage of the stationary hood, twice each revolution of thekiln, with the tubes being spaced away from the hot processed materialdischarged through the kiln ports.

Other features and objects of the invention that have been attained willappear from the more detailed description to follow with reference to anembodiment of the present invention shown in the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 of the accompanying drawing is afragmentary side elevation, partly in section, of a rotary kiln with agas delivery manifold and processed material discharge assemblyaccording to the present invention;

FIG. 2 is an end view taken along line lIlI in FIG. 1 and viewing thestructure in the direction indicated by arrows; and

- FIG. 3 is a fragmentary side elevation in section, taken along lineIII-III in FIG. 2, viewing the structure in the direction indicated byarrows and with a stationary hood, shown in FIGS. 1 and 2, eliminatedfrom this view.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 of thedrawings, a rotary kiln having a cylindrical shell 1 is supported in aconventional manner (not shown) to rotate about a central axis A-A. Asshown in FIG. 3, the shell 1 is refractory lined and provided with apair of radial discharge ports 2, 3 adjacent the end 4 of kiln shell 1and (see FIGS. 2, 3) the ports 2, 3 are circumferentially spaced apartI80", for discharging processed material downwardly therethrough; i.e.,gravity discharge, twice each revolution of the kiln shell 1.

Referring to FIGS. 1 and 3, a rotary firing hood 5 is mountedconcentrically about the discharge end 4 of the kiln shell 1 andconnected thereto to rotate with the kiln shell 1 about the central axisA-A. Hood 5 is provided with a rear wall 6 at the end 4 of kiln shell 1,and a forward wall 7 axially spaced along the kiln shell 1 from the rearwall 6. The walls 6, 7 are axially spaced apart by axially extendingtubular elements 8 arranged radially outward of kiln shell 1. The rearwall 6 is provided with a neck 6a through which a conventional main kilnburner 9 projects concentrically to axis A--A into firing hood 5. Rearwall 6 therefore encloses the discharge end 4 of kiln shell I about theburner 9. The rear wall neck 6a is provided with a flange 10 attachedthereto which therefore rotates with rear wall 6. The flange 10 issealed relative to the stationary burner 9 by a bellows seal 11. Thebellows seal 11 has a flange 12 which does not rotate, and which engagesthe rotating flange 10, to provide a friction seal between thestationary burner 9 and the rotating neck 6a of rear wall 6.

Referring to FIG. 1, burner 9 has two branches 16, 17 with branch 16being adapted for connection to a source of primary air (not shown) andbranch 17 being adapted for connection to a source of primary fuel gas(not shown). The burner 9 with its branches I6, 17, is mounted on aretractable burner support assembly 18. A first annular gas manifold box20 is provided around the rear wall neck 60 and between rear wall 6 andflange 10. The box 20 is adapted for connection to a second stationarysource of fuel gas, conduit 21, at a coupling 22. A second annular gasmanifold box 23 is provided between the manifold box 20 and rear wall 6,and box 23 is adapted for connection to a second stationary source ofair, conduit 24, at a coupling 25. The construction of the manifoldboxes 20 and 23 will be described with reference to FIG. 3.

As shown in FIG. 3, the first annular gas manifold box 20 has a firstportion which is a cylindrical sleeve 28 with a port 29 in registry withthe coupling 22, and sleeve 28 is fitted over and encloses a secondportion of box 20 which is an annular channel 30. The channel 30comprises a pair of axially spaced annular walls 31, 32 attached to acylindrical collar 33 fitted around a neck portion 6a of rear wall 6,through which the burner 9 projects. As will appear from the descriptionto follow, the second portion; i.e., the channel 30, rotates with theend wall 6. Channel 30 therefore rotates within the inner periphery ofthe nonrotating sleeve 28. Annular seals 34, 35 are provided between thechannel 30 (which rotates) and the sleeve 28 (which does not rotate).The second annular gas manifold box 23 is constructed in a mannersimilar to the box 20 but the annular configuration of box 23 is oflarger diameter than box 20, for reasons that shall appear as thedescription of the apparatus proceeds, and box 23 is proportionatelylarger than box 20 to accommodate air in larger volumes than the fuelgas delivered to box 20. The box 23 has a first portion which is acylindrical sleeve with a port 41 in registry with the coupling 25 andsleeve 40 is fitted over and encloses a second portion which is anannular channel 42. The channel 42 comprises a pair of axially spacedannular walls 43, 44 attached to a cylindrical collar 45 radially spacedaround the neck portion 6a of rear wall 6. As will appear from thedescription to follow, the second portion of box 23, i.e., the channel42, also rotates with end wall 6. Channel 42 therefore rotates withinthe inner periphery of the nonrotating sleeve 40. Annular seals 46, 47are provided between the channel 42 (which rotates) and the sleeve 40(which does not rotate).

Referring to FIGS. 1 and 3, a first plurality of tubes 50 and a secondplurality of tubes 51 are provided which each have a first section 52,53 respectively, mounted on the outer periphery of kiln shell 1 parallelto the central axis A-A. The tubes 50 are provided to deliver fuel gasand tubes 51 are provided to deliver air, to kiln shell burners 54, onlyone of which is shown (see FIG. I) and which may be such as aredisclosed in US Pat. No. 3,029,l4l. The first sections 52, 53 of tubes50, 51 project through the tubular elements 8 which extend between thewalls 6, 7 of rotary hood 5. The tubes 50 have a second section 55projecting radially inward along the outer surface of rear wall 6 and athird section 56 projecting axially away from rear wall 6. The thirdsection 56 of tubes 50 extends parallel to axis A-A radially outward ofneck 60 of rear wall 6 and radially inward of the second annular gasmanifold box 23, and into gas communicating connection with the firstannular gas manifold box 20. As shown in FIG. 3 section 56 extendsaxially along the outer periphery of the neck 6a and inward of thecylindrical collar 45, and is connected to the annular wall 32 of thesecond portion of box 20, i.e., channel 30, to discharge gas into thebox 20. The tubes 51 have a second section 57 projecting radially inwardand along the outer surface of rear wall 6 and a third section 58projecting axially away from rear wall 6. The third section 58 of tubes51 extends parallel to axis A-A radially outward of the third sections56 of tubes 50 and into air communicating connection with the secondannular gas manifold box 23. The sections 58 are connected to theannular wall 44 of the second portion of box 23, i.e., channel 42, todischarge air from the box 23. Since the tubes 50, 51 are mounted onkiln shell 1 to rotate therewith and the annular channels 30, 42, areconnected to the tubes 50, 51, the channels 30, 42 are carried by thetubes to rotate relative to the sleeves 28, 40 which are connected tostationary supply conduits 21, 24 and therefore carried in a positionfixed in space.

Referring to FIG. 2, the first sections 52, 53 of the tubes 50, 51, arearranged in two groups. The tube sections 52, 53 of a first of thegroups are identified in FIG. 2 as tube sections 520 and 53a, and tubesections 52, 53 of a second of the groups are identified in FIG. 2 astube sections 52b and 53b. The tube sections 52a and 53a are arranged,alternately, along one side of the periphery of kiln shell I. Theindividual tube sections 52a and 530 are circumferentially spaced apartfrom each other and the sections 520, 53a are grouped relative to thecircumference of kiln shell 1 to be circumferentially between thedischarge ports 2, 3 in kiln shell 1. Likewise, the tube sections 52band 53b are arranged, alternately, along the side of kiln shell 1opposite to tube sections 520 and 53a, and the tube sections 52b, 53bare also grouped to be circumferentially between the discharge ports 2,3. Thus none of the tube sections 52a, 53a or 52b, 53b pass axially overthe ports 2, 3 in kiln shell 1.

Referring to FIGS. 2 and 3, the tubular elements 8 through which thetube sections 52a, 53a pass, are surrounded by a cast refractory shroud60. As shown in FIG. 2, the tubular elements through which the tubesections 52b, 53b pass are also surrounded by a cast shroud 61 similarto shroud 60. The shrouds 60, 61 may be fonned in place from a thick mudof refractory cement poured into suitable removable forms (not shown),after which the mud is permitted to dry and harden to a solid body. Theshrouds 60, 61 protect the tubular elements 8 from hot gases andprocessed material emitted from kiln shell ports 2 and 3, and theshrouds 60, 61 define therebetween a pair of radial discharge passages62, 63 in registry with the kiln shell ports 2 and 3.

Referring to FIGS. 1 and 2, the apparatus is provided with a stationaryhood 64 encircling the outer circumference of rotary hood 5 andstationary hood 64 defines a single downward discharge passage 65.

Referring to FIG. 1, annular seals 66, 67 are provided between thestationary hood 64 and the rotary hood 5. Each of the seals 66, 67 isprovided with an annular ring 68 connected to the rotary hood 5 torotate therewith, and an annular ring 69 pivotally connected by anactuating arm 70 to the stationary hood 64. The pivotal actuating arm 70is actuated by a weight 71 to bias ring 69 toward frictional engagementwith ring 68 to provide a friction seal between rings 68, 69.

The apparatus that has been described may be operated to processmaterial according to a variety of operations and processes, such as aredisclosed for example in US. Pat. No. 1,797,130, US. Pat. No. 3,029,141,and U.S. Pat. No. 3,182,980. In operation with the described apparatusmaterial to be processed by heat and gases supplied by burners 9 and 54,moves axially through the kiln shell ltoward the discharge end 4,because of the usual slight downward sloping alignment of kiln shell 1toward the discharge end 4. Air and fuel for the primary burner 9 issupplied through the branches l6, 17 of the burner 9. Fuel for the kilnshell burners 54 is supplied through the stationary conduit 21 to thefirst portion of box 20, i.e., nonrotating sleeve 28 of box 20, and tothe second portion of box 20, i.e., annular channel 30 which rotateswith kiln shell 1. From channel 30 the fuel gas passes through thesections 56, 55 and 52 of the first plurality of tubes 50. Air for thekiln shell burner 54 is supplied through the stationary conduit 24 tothe first portion of box 23, i.e., nonrotating sleeve 40 of box 23, andto the second portion of box 23, i.e., channel 42 which rotates withkiln shell 1. From channel 42 the air passes through the sections 58, 57and 53 of the second plurality of tubes 51. After the material in kilnshell 1 has been processed and arrives at the discharge end 4 of kilnshell 1, the material is discharged from the kiln twice each revolutionof kiln shell 1 and rotary hood'5, through ports land 3 and between theshrouds 60, 61 enclosing the two groups of tube sections 52a, 53a and52b, 53b, to fall downwardly through the stationary hood dischargepassage 65. 7

With the described apparatus the foregoing operation is achieved withsealed annular gas manifold boxes 20, 23 being of smaller diameter thanthe kiln shell 1. In fact, the annular seals 34, 35 for the fuel box areonly slightly larger in diameter than the neck 6a of rear wall 6 andtherefore can be constructed to effectively seal against loss of costlycombustible fuelgases utilized in such as the described operations.Furthermore, the tube sections 52 and 53 in tubular elements 8 that passthrough the rotary firing hood 5 are not directly exposed to theatmosphere within the kiln or the hot and usually abrasive processedmaterial discharging from the kiln.

From the foregoing detailed description of the present invention it hasbeen shown how the objects of the present invention have been attainedin a preferred manner. However, modification and equivalents of thedisclosed concepts such as readily occur to those skilled in the art areintended to be inv cluded in the scope of this invention. Thus, thescope of the invention is intended to be limited only by the scope ofthe claims such as are or may hereafter be, appended hereto.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. An apparatus comprising:

a. a cylindrical rotary kiln shell having a plurality of kiln shellmounted burners each projecting radially inward through the kiln shell,and the kiln shell having a radial discharge 'portthrough the shellthereof adjacent one end of the kiln shell for discharging processedmaterial from the kiln shell;

b. a rotary firing hood mounted concentrically about the end of the kilnshell and connected thereto to rotate with thekiln shell about a centralaxis through the kiln shell, with the rotary firing hood having a rearwall closing the adjacent end of the kiln shell;

c. a first annular gas manifold box concentric to the central axis andaxially'spaced away from the kiln shell and hood rear wall adapted forconnecting a stationary gas source to the plurality of kiln shellmounted burners, and said annular box having an outer circumference of adiameter smaller than the diameter of the kiln shell; and

d. a first plurality of gas conducting tubes each having a first sectionmounted on the outer periphery of the kiln shell with each said tubefirst section connected on one end to at least one of said kiln shellmounted burners and each of the first sections being parallel to thecentral axis and circumferentially spaced away from the radial dischargeport in the rotary kiln shell, with the first section of each tubeextending through the rotary hood and rear wall thereof, and each tubehaving a second section projecting radially inward along the outersurface of the rear wall and a third section projecting axially awayfrom the rear wall into connectionwith the annular gas manifold box forconducting gas from the annular gas manifold box into the gas conductingtubes to the shell mounted burners, and with the gas conducting tubesspaced away from exposure to processed, material discharged from thekiln shell through the radial discharge port.

2. An apparatus according to claim 1 having a stationary hood encirclingthe outer circumference of the rotary hood and defining a downwarddischarge passage through which processed material from the rotary kilnshell is discharged upon rotation of the kiln shell to bring the kilnshell radial discharge port in registry with the stationary hooddischarge passage.

3. An apparatus according to claim 1 having a second annular gasmanifold box with an outer diameter smaller than the diameter of thekiln shell but larger than the outer diameter of the first annular box,said second annular box being between the first gas manifold box and therear wall of the rotary hood, concentric about the central axis and withan inner periphery radially outward of the third sections of the firstplurality of gas tubes, and a second plurality of gas conducting tubeseach having a first section mounted on the periphery of the kiln shellwith each said tube first section connected on one end to at least oneof the kiln shell mounted burners and each of the tube first sectionsbeing parallel to the central axis and circumferentially spaced awayfrom the discharge port in the rotary kiln shell, with the first sectionof each tube of the second plurality extending through the rotary hoodand rear wall thereof, and each tube of the second plurality having asecond section projecting radially inward along the outer surface of therear wall and a third section projecting axially away from the rear wallinto connection with the second annular gas manifold box.

4. An apparatus according to claim 3 having a main burner concentric tothe central axis of the kiln and projecting through a central openingdefined by the first and second annular gas manifold boxes, through therear wall of the rotary hood, and into the adjacent end of the rotarykiln shell.

5. In an apparatus according to claim 1, the rotary kiln shell having apair of radial discharge ports circumferentially spaced apart, and thefirst sections of the gas conducting tubes being circumferentiallyarranged in two groups with both groups arranged circumferentiallyspaced from both discharge ports, to discharge processed materialbetween the groups of tubes twice each revolution of the rotary kiln.

6. In an apparatus according to claim 3, the tubes of the first andsecond pluralities thereof being arranged with each tube of the firstplurality being circumferentially located between a pair of tubes of thesecond plurality.

7. In an apparatus according to claim 1, the first annular gas manifoldbox having a first portion comprising a cylindrical sleeve with a portadapted to be connected to a stationary gas source, and the firstannular gas manifold box having a second portion comprising an annularchannel defined by a cylindrical collar with a pair of axially spacedradially extending annular walls, the cylindrical sleeve being arrangedto engage the outer periphery of the annular walls to enclose theannular channel of the said first annular gas manifold box and the thirdsection of each gas conducting tube being connected to the annularchannel for receiving gas there-from.

8. In an apparatus according to claim 3, each annular gas manifold boxhaving a first portion comprising a cylindrical nular gas manifold box,and the third section of each tube of the first plurality of tubes beingconnected to the annular channel of the first manifold box and the thirdsection of each tube of the second plurality of tubes being connected tothe annular channel of the second manifold box.

t I 1 k I

1. An apparatus comprising: a. a cylindrical rotary kiln shell having aplurality of kiln shell mounted burners each projecting radially inwardthrough the kiln shell, and the kiln shell having a radial dischargeport through the shell thereof adjacent one end of the kiln shell fordischarging processed material from the kiln shell; b. a rotary firinghood mounted concentrically about the end of the kiln shell andconnected thereto to rotate with the kiln shell about a central axisthrough the kiln shell, with the rotary firing hood having a rear wallclosing the adjacent end of the kiln shell; c. a first annular gasmanifold box concentric to the central axis and axially spaced away fromthe kiln shell and hood rear wall adapted for connecting a stationarygas source to the plurality of kiln shell mounted burners, and saidannular box having an outer circumference of a diameter smaller than thediameter of the kiln shell; and d. a first plurality of gas conductingtubes each having a first section mounted on the outer periphery of thekiln shell with each said tube first section connected on one end to atleast one of said kiln shell mounted burners and each of the firstsections being parallel to thE central axis and circumferentially spacedaway from the radial discharge port in the rotary kiln shell, with thefirst section of each tube extending through the rotary hood and rearwall thereof, and each tube having a second section projecting radiallyinward along the outer surface of the rear wall and a third sectionprojecting axially away from the rear wall into connection with theannular gas manifold box for conducting gas from the annular gasmanifold box into the gas conducting tubes to the shell mounted burners,and with the gas conducting tubes spaced away from exposure to processedmaterial discharged from the kiln shell through the radial dischargeport.
 2. An apparatus according to claim 1 having a stationary hoodencircling the outer circumference of the rotary hood and defining adownward discharge passage through which processed material from therotary kiln shell is discharged upon rotation of the kiln shell to bringthe kiln shell radial discharge port in registry with the stationaryhood discharge passage.
 3. An apparatus according to claim 1 having asecond annular gas manifold box with an outer diameter smaller than thediameter of the kiln shell but larger than the outer diameter of thefirst annular box, said second annular box being between the first gasmanifold box and the rear wall of the rotary hood, concentric about thecentral axis and with an inner periphery radially outward of the thirdsections of the first plurality of gas tubes, and a second plurality ofgas conducting tubes each having a first section mounted on theperiphery of the kiln shell with each said tube first section connectedon one end to at least one of the kiln shell mounted burners and each ofthe tube first sections being parallel to the central axis andcircumferentially spaced away from the discharge port in the rotary kilnshell, with the first section of each tube of the second pluralityextending through the rotary hood and rear wall thereof, and each tubeof the second plurality having a second section projecting radiallyinward along the outer surface of the rear wall and a third sectionprojecting axially away from the rear wall into connection with thesecond annular gas manifold box.
 4. An apparatus according to claim 3having a main burner concentric to the central axis of the kiln andprojecting through a central opening defined by the first and secondannular gas manifold boxes, through the rear wall of the rotary hood,and into the adjacent end of the rotary kiln shell.
 5. In an apparatusaccording to claim 1, the rotary kiln shell having a pair of radialdischarge ports circumferentially spaced 180* apart, and the firstsections of the gas conducting tubes being circumferentially arranged intwo groups with both groups arranged circumferentially spaced from bothdischarge ports, to discharge processed material between the groups oftubes twice each revolution of the rotary kiln.
 6. In an apparatusaccording to claim 3, the tubes of the first and second pluralitiesthereof being arranged with each tube of the first plurality beingcircumferentially located between a pair of tubes of the secondplurality.
 7. In an apparatus according to claim 1, the first annulargas manifold box having a first portion comprising a cylindrical sleevewith a port adapted to be connected to a stationary gas source, and thefirst annular gas manifold box having a second portion comprising anannular channel defined by a cylindrical collar with a pair of axiallyspaced radially extending annular walls, the cylindrical sleeve beingarranged to engage the outer periphery of the annular walls to enclosethe annular channel of the said first annular gas manifold box and thethird section of each gas conducting tube being connected to the annularchannel for receiving gas there-from.
 8. In an apparatus according toclaim 3, each annular gas manifold box having a first portion comprisinga cylindrical sleeve with a port adapted to be connected to a stationarygas source, and each annular gas manifold box having a second portioncomprising an annular channel defined by a cylindrical collar with apair of axially spaced radially extending annular walls, the cylindricalsleeve of each said box being arranged to engage the outer periphery ofthe annular walls of each said box to enclose the annular channel ofeach said annular gas manifold box, and the third section of each tubeof the first plurality of tubes being connected to the annular channelof the first manifold box and the third section of each tube of thesecond plurality of tubes being connected to the annular channel of thesecond manifold box.